Galvanically isolated DC/DC converter and method of controlling a galvanically isolated DC/DC converter

Abstract

A galvanically isolated DC/DC converter includes a first and a second side converter circuit coupled between a pair of first side DC terminals and a pair of second side DC terminals, respectively. The first side converter circuit has a first and a second switching element, each including a switch and a diode. When the DC/DC converter is in power transfer operation from the second side DC terminals to the first side DC terminals, the second side converter circuit alternates between two power transfer states. A conductive state of the diode of one of the first and second switching elements is the result of one of the two power transfer states. The first side converter circuit is controlled such that the switch of the respectively other of the first and second switching elements is closed for an adaptation interval before the one of the two power transfer states starts.

The invention claimed is: 
     
       1. A galvanically isolated DC/DC converter, comprising:
 at least one first side converter circuit coupled between a pair of first side DC terminals, the first side converter circuit having at least a first and a second switching element, with each of the first and second switching elements comprising a switch and a diode connected in parallel, and 
 at least one second side converter circuit coupled between a pair of second side DC terminals, 
 wherein, when the DC/DC converter is in power transfer operation from the pair of second side DC terminals to the pair of first side DC terminals, the second side converter circuit is adapted to alternate between two power transfer states, wherein a conductive state of the diode of one of the first and second switching elements is the result of one of the two power transfer states, with the first side converter circuit being controlled such that the switch of the respectively other of the first and second switching elements is closed for an adaptation interval (T P ) prior to a beginning of the one of the two power transfer states, 
 wherein the first side converter circuit is controlled such that the adaptation interval (T P ) ends a preset commutation time (T K ) before the beginning of the one of the two power transfer states, and 
 wherein the preset commutation time (T K ) is chosen such that the conductive state of the diode of the one of the first and second switching elements is present at the beginning of the one of the two power transfer states. 
 
     
     
       2. The galvanically isolated DC/DC converter according to  claim 1 , wherein the first side converter circuit is an H bridge circuit, which comprises the first and second switching elements and further comprises a third and a fourth switching element, with each of the third and fourth switching elements comprising a switch and a diode in parallel, wherein a conductive state of the diodes of two of the first to fourth switching elements is the result of one of the two power transfer states, with the first side converter circuit being controlled such that the switches of the respectively other two of the first to fourth switching elements are closed for the adaptation interval (T P ) prior to the beginning of the one of the two power transfer states. 
     
     
       3. The galvanically isolated DC/DC converter according to  claim 1 , wherein the second side converter circuit is adapted to be in a state of no power transfer between the two power transfer states, with the adaptation interval (T P ) being during the state of no power transfer. 
     
     
       4. The galvanically isolated DC/DC converter according to  claim 1 , wherein the adaptation interval (T P ) has a preset duration. 
     
     
       5. The galvanically isolated DC/DC converter according to  claim 1 , wherein a duration of the adaptation interval (T P ) is dependent on the operating point of the DC/DC converter. 
     
     
       6. The galvanically isolated DC/DC converter according to  claim 1 , wherein each of the switches of the first side converter circuit is an insulated-gate bipolar transistor. 
     
     
       7. The galvanically isolated DC/DC converter according to  claim 1 , wherein the first side converter circuit has voltage source characteristics. 
     
     
       8. The galvanically isolated DC/DC converter according to  claim 1 , wherein the second side converter circuit has current source characteristics. 
     
     
       9. The galvanically isolated DC/DC converter according to  claim 1 , wherein the second side converter circuit has two parallel branches between the pair of second side DC terminals, each branch comprising an inductance element and a second side switching element. 
     
     
       10. The galvanically isolated DC/DC converter according to  claim 9 , wherein each of the second side switching elements is a MOSFET. 
     
     
       11. The galvanically isolated DC/DC converter according to  claim 1 , wherein the second side converter circuit is an H bridge circuit or a transformer center tapped circuit having at least two second side switching elements. 
     
     
       12. The galvanically isolated DC/DC converter according to  claim 1 , wherein the second side converter circuit has at least two second side switching elements, with each of a first one and a second one of the second side switching elements comprising a switch and a diode connected in parallel,
 wherein, when the DC/DC converter is in forward power transfer operation from the pair of first side DC terminals to the pair of second side DC terminals, the diodes of the first one and the second one of the second side switching elements are alternately in a conductive state, with each of the first one and the second one of the second side switching elements being controlled such that a closed state of the respective switch extends beyond a transitioning of the diode of the same second side switching element from the conductive state to a blocking state. 
 
     
     
       13. The galvanically isolated DC/DC converter according to  claim 12 , wherein the respective switch of each of the first one and the second one of the second side switching elements is controlled to condition a slope of a discharge current of the diode of the same second side switching element during the transitioning thereof from the conductive state to the blocking state. 
     
     
       14. The galvanically isolated DC/DC converter according to  claim 12 , wherein each of the first one and the second one of the second side switching elements is controlled such that the respective switch is in the conductive state during substantially the whole time the diode of the same second side switching element is in the conductive state. 
     
     
       15. The galvanically isolated DC/DC converter according to  claim 12 , wherein the first side converter circuit is adapted to alternate between two forward power transfer states (PWM 1 / 4 , PWM 2 / 3 ), wherein each forward power transfer state leads to the conductive state of one of the diodes of the first one and the second one of the second side switching elements, with each of the first one and the second one of the second side switching elements being controlled such that the respective switch is opened a preset lag time (T N ) after the respective one of the two forward power transfer states is entered that leads to the conductive state of the diode of the other second side switching element. 
     
     
       16. The galvanically isolated DC/DC converter according to  claim 12 , wherein the first side converter circuit is adapted to alternate between two forward power transfer states (PWM 1 / 4 , PWM 2 / 3 ), wherein each forward power transfer state leads to the conductive state of one of the diodes of the first one and the second one of the second side switching elements, with each of the first one and the second one of the second side switching elements being controlled such that the respective switch is closed a preset delay time (T V ) after the respective one of the two forward power transfer states is entered that leads to the conductive state of the diode of the same second side switching element. 
     
     
       17. The galvanically isolated DC/DC converter according to  claim 16 , wherein the preset delay time (T V ) is greater than the preset lag time (T N ). 
     
     
       18. The galvanically isolated DC/DC converter according to  claim 1 , wherein the second side converter circuit is coupled to a protection circuit. 
     
     
       19. The galvanically isolated DC/DC converter according to  claim 18 , wherein the second side converter circuit comprises two second side switching elements and the protection circuit comprises a voltage source and two protection diodes coupled to the voltage source, with each of the second side switching elements being coupled to one of the two protection diodes. 
     
     
       20. The galvanically isolated DC/DC converter according to  claim 19 , wherein the voltage source is coupled to one of the pair of second side DC terminals or to one of the pair of first side DC terminals. 
     
     
       21. The galvanically isolated DC/DC converter according to  claim 1 , wherein the at least one first side converter circuit is a plurality of first side converter circuits connected in series between the pair of first side DC terminals and wherein the at least one second side converter circuit is a plurality of second side converter circuits connected in parallel between the pair of second side DC terminals. 
     
     
       22. The galvanically isolated DC/DC converter according to  claim 21  comprising a plurality of transformers, with each transformer coupling one of the first side converter circuits to one of the second side converter circuits. 
     
     
       23. The galvanically isolated DC/DC converter according to  claim 1 , wherein, in operation, a desired operating voltage across the pair of first side DC terminals is at least 10 times greater than an operating voltage across the pair of second side DC terminals. 
     
     
       24. The galvanically isolated DC/DC converter according to  claim 1 , wherein, in operation, a desired operating voltage across the pair of first side DC terminals is between 400V and 800V, preferably between 500V and 700V. 
     
     
       25. The galvanically isolated DC/DC converter according to  claim 1 , wherein, in operation, an operating voltage across the pair of second side DC terminals is between 10V and 40V, preferably between 20V and 30V. 
     
     
       26. A method of controlling a galvanically isolated DC/DC converter, which comprises at least one first side converter circuit coupled between a pair of first side DC terminals and at least one second side converter circuit coupled between a pair of second side DC terminals, wherein the first side converter circuit has at least a first and a second switching element, with each of the first and second switching elements comprising a switch and a diode connected in parallel, and wherein the second side converter circuit is controlled to alternate between two power transfer states for transferring power from the pair of second side DC terminals to the pair of first side DC terminals, the method comprising the steps of:
 (a) operating the second side converter circuit in one of the two power transfer states, with the one of the two power transfer states leading to the diode of a particular one of the switching elements to be in a conductive state, 
 (b) ending the one of the two power transfer states and putting the second side converter circuit in a state of no power transfer, 
 (c) closing the switch of the particular one of the switching elements for an adaptation interval (T P ), and 
 (d) putting the second side converter circuit in the other one of the two power transfer states, with the other one of the two power transfer states leading to the diode of the other one of the switching elements to be in a conductive state, 
 wherein step (d) takes place a preset commutation time (T K ) after an end of the adaptation interval T P ) and wherein the preset commutation time (T K ) is chosen such that the conductive state of the diode of the other one of the switching elements is present at the beginning of the other one of the two power transfer states. 
 
     
     
       27. The method according to  claim 26 , wherein an amount of power transfer is controlled by a duration of the two power transfer states.